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Thu, 16 Jul 2020 05:37:18 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 4522311385E0; Thu, 16 Jul 2020 07:37:17 +0200 (CEST) From: Markus Armbruster To: David Gibson Subject: Re: Slow down with: 'Make "info qom-tree" show children sorted' References: <20200527084754.7531-1-armbru@redhat.com> <20200527084754.7531-3-armbru@redhat.com> <49bea110-0a3d-5a40-6647-67b116fb41b5@redhat.com> <5e967e5f-8ae5-01cc-0dfe-f22e0f03b6b3@redhat.com> <87y2nvanya.fsf@dusky.pond.sub.org> <794f6901-5fe3-f7a1-45e7-f277f687cb6b@redhat.com> <87v9iz7cxl.fsf@dusky.pond.sub.org> <20200713111344.23c1b313@umbus.fritz.box> <874kqbbdft.fsf@dusky.pond.sub.org> <20200716095926.74caee16@umbus.fritz.box> Date: Thu, 16 Jul 2020 07:37:17 +0200 In-Reply-To: <20200716095926.74caee16@umbus.fritz.box> (David Gibson's message of "Thu, 16 Jul 2020 09:59:26 +1000") Message-ID: <87a700rpf6.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=207.211.31.81; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/16 01:37:26 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , Thomas Huth , berrange@redhat.com, ehabkost@redhat.com, Alex =?utf-8?Q?Benn=C3=A9e?= , mark.cave-ayland@ilande.co.uk, qemu-devel@nongnu.org, Greg Kurz , =?utf-8?Q?C=C3=A9dr?= =?utf-8?Q?ic?= Le Goater , Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-D?= =?utf-8?Q?aud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" David Gibson writes: > On Mon, 13 Jul 2020 18:13:42 +0200 > Markus Armbruster wrote: > >> David Gibson writes: >> >> [...] >> [...] >> [...] >> [...] >> [...] >> [...] >> [...] >> [...] >> [...] >> [...] >> >> >> >> The surprising part is that n turns out to be large enough for n^2 to >> >> matter *that* much. >> > >> > Is this another consequence of the ludicrous number of QOM objects we >> > create for LMB DRCs (one for every 256MiB of guest RAM)? Avoiding that >> > is on my list. >> >> You're talking about machine pseries, I presume. > > Yes. > >> With >> print_qom_composition() patched to print the number of children, I get >> >> $ echo -e 'info qom-tree\nq' | ../qemu/bld/ppc64-softmmu/qemu-system-ppc64 -S -display none -M pseries -accel qtest -monitor stdio | grep '###' | sort | uniq -c | sort -k 3n >> 360 ### 0 children >> 5 ### 1 children >> 5 ### 2 children >> 2 ### 3 children >> 1 ### 4 children >> 1 ### 15 children >> 1 ### 16 children >> 1 ### 18 children >> 1 ### 37 children >> 1 ### 266 children >> >> The outlier is >> >> /device[5] (spapr-pci-host-bridge) >> >> due to its 256 spapr-drc-pci children. > > Right, that's one for each possible PCI slot on the bus. That will be > reduced by the idea I have in mind for this, but... > >> I found quite a few machines with similar outliers. ARM machines nuri >> and smdkc210 together take the cake: they each have a node with 513 >> children. >> >> My stupid n^2 sort is unnoticable in normal, human usage even for n=513. > > ... as you say, 256 shouldn't really be a problem. I was concerned > about LMB DRCs rather than PCI DRCs. To have that show up, you might > need to create a machine with a large difference between initial memory > and maxmem - I think you'll get a DRC object for every 256MiB in there, > which can easily get into the thousands for large (potential) memory > VMs. Okay, I can reproduce: with -m 256,128G, /machine has 549 children, of which 511 are spapr-drc-lmb. > I don't know what the config was that showed up this problem in the > first place, and whether that could be the case there. Thomas reported device-introspect-test -m slow has become much slower for ppc64. Bisection traced it to my commit e8c9e65816 "qom: Make "info qom-tree" show children sorted". Uses default memory size, no spapr-drc-lmb as far as I remember. >> > Though avoiding a n^2 behaviour here is probably a good >> > idea anyway. >> >> Agreed. Patch posted: Subject: [PATCH for-5.1 5/5] qom: Make info qom-tree sort children more efficiently Message-Id: <20200714160202.3121879-6-armbru@redhat.com>